The present invention is generally directed to encapsulated compositions, and more specifically the present invention is directed to processes for the preparation of encapsulated toners wherein annealing and/or heat spheroidization is utilized for obtaining polymeric toner shells. Specifically, the present invention is directed to processes for encapsulated toner compositions wherein the shells thereof are obtained by interfacial polymerization and heat spheroidization, which shells are comprised of, for example, thermotropic liquid crystalline components as illustrated in U.S. Pat. No. 4,543,313, the disclosure of which is totally incorporated herein by reference; low melting polyesters, polyamides, polyureas, polyurethanes, polyester amides, and the like. Thus, in one embodiment, the process of the present invention comprises providing a core monomer or monomers, a colorant, shell monomers, a polymer or polymers, and a free radical initiator; dispersing the aforementioned core components in water containing a surfactant, an antifoaming agent and a phase transfer agent; adding shell monomers, including comonomers to the aqueous phase; polymerizing the shell monomers and heat spheroidizing thereby resulting in a polymeric shell with a softening point equal to or slightly above the temperature utilized for polymerization of the core material. The formed shell softens and anneals during the heat polymerization of the core monomers at temperatures of from, for example, about 40.degree. to about 140.degree. C., and preferably from about 65.degree. to about 90.degree. C., enabling encapsulated particles, especially toner compositions with smooth spherical morphologies. Also, the aforementioned annealing, or heat spheroidization process permits toner compositions with shells of more uniform characteristics. Thus, shells formed by an interfacial polymerization process at room temperature have, in most situations, a lower density in the inner shell as opposed to the outer shell. This results as shell formation is dependent on the diffusion characteristics of the monomers at the interface between the core and the shell. It is believed that with the process of the present invention wherein, for example, heat spheroidization is selected there results the formation of a more uniform shell. The aforementioned heat spheroidization process also permits encapsulated toner compositions in which the pigments are passivated by the shell, that is the heat spheroidization allows the formation of a very uniform polymeric coating over the core materials resulting in a toner with desirable electrical properties dependent on the properties of the coating for example. Moreover, additives can be incorporated into the shell as comonomers during the interfacial polymerization process. These additives modify in a controlled manner the electrical properties of the toner. It is also believed that the toner electrical properties can be modified by adding pigments such as carbon black and graphite to the surface, this addition being done during the heat spheroidization process in the presence of said pigments. Thus, with the process of the present invention in one embodiment there are obtained heat fusible toner compositions comprised of a polymeric core component, and thereover a thermotropic liquid crystalline polymeric shell. Also, the toner compositions of the present invention which in some embodiments possess core melting temperatures between about 60.degree. to about 140.degree. C. and preferably below 120.degree. C., and shell melting temperatures between about 60.degree. to about 140.degree. C. and preferably between 80.degree. and 120.degree. C., permit a life extension of the fuser roll incorporated into electrostatographic, especially xerographic, imaging processes in that, for example, lower fusing energies can be selected, that is fusing can be effected at temperatures not exceeding 120.degree. C. (fuser setting); and further the toner compositions of the present invention can be changed from about a -25 microcoulombs per gram to about a +25 microcoulombs per gram or other preselected values irrespective of the pigment selected for the core. This can be achieved, for example, with the appropriate choice of shell materials, shell additives, external additives and carriers for encapsulated toners obtained by the process of the present invention.
Of particular importance with respect to the toner compositions of the present invention is the enablement of shell melting at, for example, from about 60.degree. C. to about 140.degree. C., and preferably from about 80.degree. to 120.degree. C., which shell retains its characteristics, that is for example it does not fracture prematurely. Furthermore, when thermotropic liquid crystalline polymer shells are selected the encapsulated toners possess other important characteristics including, for example, the melting thereof over a narrow temperature interval; and wherein there is a substantial decrease in the mesophase melt viscosity before the clearing temperature, which is above the melting point of the resins or monomers subsequent to polymerization selected for the toner core.
The aforementioned toner compositions are useful for permitting the development of images in electrostatographic systems, inclusive of electrostatic imaging and printing processes. Also, the toner compositions prepared in accordance with the process of the present invention have shells with the advantages indicated herein including smooth surfaces with substantially no pinholes, or the avoidance of all pinholes in some instances, and a uniform continuous thickness around the core of the particles. This results in improved mechanical properties of the toner as compared to the properties of encapsulated toners prepared with a process not involving heat spheroidization. The shells prepared by the process described herein also have the added advantage of providing a superior insulation layer between the core materials and the outside of the particles, which results in improved passivating properties in some instances.
There is disclosed in Konishiroku Japanese Publication Nos. 60/198554 A2, 60/198555 A2, and Canon Japanese Publication No. 61/65260 A2 heat fusible encapsulated toner compositions in which the shell of the encapsulated toner is prepared by an overcoating process involving the use of an organic solvent and polymeric materials of high melting points with a sufficient glass transition temperature to provide good blocking properties for these compositions. The toner compositions of the present invention can contain similar core polymeric components, that is for example styrene acrylate and styrene methacrylate polymers; however, these cores are encapsulated, for example within a thermotropic liquid crystalline polymer component, which component is not illustrated in the aforementioned publications; and further the shells of the present invention are obtained by a heat spheroidization process. Accordingly, the toner compositions of the present invention have the advantages as indicated herein in that, for example, the thermotropic liquid crystalline shell components possess a combination of high glass transition temperatures and low melting points thereby enabling less fusing energies and reduced fixing pressures to be selected. Additionally, in contrast to the processes disclosed in the Japanese publications, the shells of the present invention are prepared by interfacial polymerization in a simplified continuous one step process wherein the core and the shell of the toner are simultaneously formulated, which process therefore is of lower cost, that is from about 15 to about 40 percent less than the aforementioned prior art processes.
With further reference to the prior art, there is disclosed in Japanese Publication No. 61/56352 A2, heat fusible encapsulated toner compositions with a core prepared by in situ free radical polymerization with an epoxy-urea shell of a very high melting temperature. These toners do not ordinarily possess low melting properties, that is they cannot be heat fixed with fusers set at temperatures as low as 120.degree. C. In contrast, the toner compositions of the present invention can be used both in conventional heat fusing imaging systems wherein high melting materials with, for example, a softening point above 100.degree. C. are required necessitating fuser temperatures of up to 180.degree. C.; and in low melt applications as the shell and the core can be formulated accordingly. Also, the toner compositions of the present invention are believed to possess improved release properties from the fuser roll because of the presence of the thermotropic liquid crystalline shell, which component has acceptable wetting characteristics with respect to the substrate, such as paper or plastic film that is selected. Furthermore, the shell materials of the present invention can be annealed or heat spheroidized at temperatures below the boiling point of water, the medium in which encapsulated toners are usually prepared. This usually cannot be accomplished with shells of very high melting points, that is higher than 140.degree. C., or crosslinked shells prepared from multifunctional monomers as opposed to the difunctional monomers used for this invention.
As a result of a patentability search, there were selected U.S. Pat. Nos. 4,345,015; 4,702,989; 4,520,091; 3,155,590; 3,567,650; 3,594,326; 3,893,932; 3,893,933 and 4,725,522. The '015 patent discloses the preparation of toner particles by heating and stirring irregularly shaped resin particles in hydrophobic silica particles of a liquid carrier such as water or mixture of water, and a water miscible organic solvent that does not dissolve the resin, with heating to a temperature at which the resin particles soften until they become spherical or almost spherical, followed by cooling of the dispersion and separating and drying the toner particles. In the '989 patent, there are illustrated, reference the Abstract of the Disclosure, pressure fixable toners prepared by the steps as indicated including heating the dispersion to evaporate off the solvent, dispersing the resulting encapsulated toner in a lower alcohol to remove the solvent remaining within the encapsulated toner, and thereafter drying the toner. Further details concerning this process are outlined in column 4, beginning at line 26, and note particularly column 4, beginning at line 61, and column 8, lines 15 to 28. Also of interest is Example I in column 10, lines 30 to 55. The '091 patent illustrates microcapsule toners which are spray dried at about 110.degree. to 170.degree. C., and further is treated by heating for a prolonged period of time at 80.degree. to 150.degree. C., reference column 3, beginning at line 14, for example. Also, note the disclosure in column 10, beginning at line 52, wherein it is indicated that the dried encapsulated toner is preferably heated to further improve its powder characteristics. The temperature for heating the dried encapsulated toner preferably ranges from 50.degree. to 300.degree., and more preferably from 80.degree. to 150.degree. C. The other references listed were selected as being primarily of background interest.
Additionally, there are disclosed in Japanese Publication No. 61/118758 A2, Japanese Publication No. 59/218460 A2, Japanese Publication No. 61/28957 A2, Japanese Publication No. 60/175057 A2, and Japanese Publication No. 60/166958 A2 heat fusible toner compositions prepared by suspension polymerization. Examples illustrating colored photocapsule toners include U.S. Pat. Nos. 4,399,209; 4,482,624; 4,483,912 and 4,397,483. More specifically, the '483 patent illustrates encapsulated toner materials which have applications in very specific areas such as pressure sensitive recording paper. Capsules prepared for this application are usually coated on a substrate directly from the emulsion in which they are prepared and withstand with difficulties spray drying processes, a disadvantage alleviated with the toners prepared in accordance with the process of the present invention. Furthermore, these capsules contain an organic liquid in the core which, when used in a dry development system, could result in poor fix properties. Also, the range of particle sizes prepared by the aforementioned prior art process results in the formation of pressure sensitive recording particles which are usually not acceptable for electrostatographic development systems. The process of the present invention may, however, be selected for preparing capsule materials which could be used for the purposes described in the '483 patent. In the '209, '624, and the '912 patents, there are described toner compositions with costly encapsulated radiation sensitive components thereby necessitating the need for an image forming agent.
Moreover, there is disclosed in U.S. Pat. No. 4,476,211 the preparation of electrostatographic toner materials with surface electroconductivity. Specifically, there is disclosed in the '211 patent a cold pressure fixable toner composition with polyamide, polyurea and other types of shell materials prepared by an interfacial polymerization process. The colorant selected for these compositions is generally comprised of a variety of dyes or pigments, and the core contains a polymeric material with a binder therein for retaining the colorant within the core and assisting in the fixing of the colorant onto the surface of a support medium. Examples of high boiling liquids selected for the process of the '211 patent include those boiling at temperatures higher than 180.degree. C. such as phthalic esters, phosphoric acid esters, and alkyl naphthalenes.
Furthermore, there are disclosed in U.S. Pat. No. 4,307,169 microcapsular electrostatic marking particles containing a pressure fixable core, and an encapsulating substance comprised of a pressure rupturable shell, wherein the shell, such as a polyamide, is formed by an interfacial polymerization. Additionally, there are disclosed in U.S. Pat. No. 4,407,922, pressure sensitive toner compositions obtained by interfacial polymerization processes, and comprised of a blend of two immiscible polymers selected from the group consisting of certain polymers as a hard component, and polyoctyldecylvinylether-co-maleic anhydride as a soft component. Moreover, illustrated in a copending application U.S. Ser. No. 621,307, the disclosure of which is totally incorporated herein by reference, are single component cold pressure fixable toner compositions, wherein the shell selected can be prepared by an interfacial polymerization process. A similar teaching is present in copending application U.S. Ser. No. 718,676, relating to cold pressure fixable toners, the disclosure of which is totally incorporated herein by reference. In the aforementioned application, the core can be comprised of magnetite and a polyisobutylene of a specific molecular weight encapsulated in a polymeric shell material generated by an interfacial polymerization process.
Additionally, there are illustrated in U.S. Pat. No. 4,543,313, the disclosure of which is totally incorporated herein by reference, toner compositions comprised of resin particles selected from the group consisting of thermotropic liquid crystalline polycarbonates, copolycarbonates, polyurethanes, polyesters, and copolyesters; and pigment particles. The aforementioned thermotropic liquid crystalline polymers, especially the polyesters and the polyurethanes, are useful as shells for the toner compositions of the present invention. However, the toner compositions of the '313 patent are not encapsulated and are prepared by conventional processes, such as melt blending and jetting.
There are also disclosed in copending application U.S. Ser. No. 043,265, the disclosure of which is totally incorporated herein by reference, toner compositions comprised of core components, and thereover a thermotropic liquid crystalline polymeric shell formulated by interfacial polymerization. Further, in this copending application there is described black or colored toner compositions comprised of a polymer core or polymer mixtures, and pigment particles encapsulated in a shell formulated by interfacial polymerization processes, which shell is selected from the group consisting of thermotropic liquid crystalline polyesters, polycarbonates, polyurethanes, copolycarbonates, and copolyesters, reference U.S. Pat. No. 4,543,313. Therefore, in one specific embodiment of the aforementioned copending application the toner compositions are comprised of a polymer core having dispersed therein as pigments components selected from the group consisting of black, cyan, magenta, yellow, red, magnetites, and mixtures thereof; and thereover a thermotropic liquid crystalline polymeric shell. Also, additive particles in an amount of from about 0.1 percent by weight to about 1 percent by weight, such as colloidal silicas, inclusive of Aerosils and/or metal salts or metal salts of fatty acids, inclusive of zinc stearate, can be added to the formulated encapsulated toner. Moreover, there can be incorporated into the toner compositions of the copending application charge enhancing additives in an amount of from about 1 percent to about 20 percent by weight to enable positively charged toner compositions, which additives include alkyl pyridinium halides, reference U.S. Pat. No. 4,298,672, the disclosure of which is totally incorporated herein by reference; sulfate and sulfonate compositions, reference U.S. Pat. No. 4,338,390, the disclosure of which is totally incorporated herein by reference; distearyl dimethyl ammonium methyl sulfate, reference U.S. Pat. No. 4,560,635, the disclosure of which is totally incorporated herein by reference; and the like. Furthermore, there are provided in accordance with the copending application processes for the preparation of toner compositions wherein the shell component is obtained by interfacial polymerization. One of the differences between the process of the present invention and the aforementioned copending application resides in the heat treatment of the shell materials in such a manner to induce permanent morphological changes within the shell. These changes are beneficial since they improve the materials prepared by the process of the present invention by rendering them less susceptible to cracking (more uniform thicknesses). Also, toners compositions prepared by the process of the present invention possess more uniform electrical properties and characteristics permitting their suitability for applications in which passivation of the electrical properties of the core components is needed, or desired.
In one preferred specific embodiment of the aforesaid copending application there are illustrated toner compositions comprised of a core of (1) a prepolymerized styrene-n-butylmethacrylate copolymer with a glass transition temperature of about 55.degree. C. present in an amount of from about 1 percent to about 30 percent by weight, and preferably from about 10 percent by weight to about 20 percent by weight; and an in situ polymerized styrene polymer present in an amount of from about 30 to about 50 percent by weight of the toner; and (2) a mixture of magnetite, from about 1 percent to about 60 percent by weight, and preferably from about 1 percent to about 30 percent by weight, and carbon black from about 2 percent to about 15 percent by weight, and preferably from about 3 to about 10 percent by weight, encapsulated with a polyester thermotropic liquid crystalline shell present in an amount of from about 10 percent to about 25 percent by weight. The resulting toner has a core/shell morphology with a shell thickness of from about 0.05 to about 1.0 micron. With further respect to the specific aforementioned compositions, there can be present in the core either carbon black or magnetite in an amount of from about 3 to about 8 percent, and from about 15 to about 20 percent, respectively.